1. Field of the Invention
The present invention relates to helmet mounted displays (HMDs). More particularly, it relates to the use of a common lens in a biocular or binocular HMD.
2. Description of the Prior Art
Helmet mounted displays (HMDs) are a class of image display devices that can be used to display images for military and/or recreational applications. An HMD can be monocular, biocular or binocular. HMD systems which are biocular or binocular must, by definition, supply one or more images to the two eyes of the user. In doing so, these systems make use of a partially reflective surface, usually in the form of a visor or a combiner element positioned in front of the eyes. Optics trains comprised of mirrors, lenses, and other elements of the HMD are used to manipulate the light rays and the bundles of light rays which comprise the optical field, so as to project images from an image source to the eye(s) in a manner which appears undistorted to the user.
The optical system (i.e., optics trains) of the HMD is of integral importance when designing the helmet and corresponding visor systems. This is primarily due to the fact that the HMD is mounted directly to the helmet of the wearer. In addition, the location of the HMD mounted on the helmet depends on the display surface on which the HMD is to project its images. The positioning of this added mass on the exterior surface of the helmet can have a negative effect on the wearer depending on the location of the same. In the present case, the helmet visor is the surface on which the HMD is to project its image. As such, the HMD optics trains and their location are dependent on the helmet visor and its physical and optical properties, along with the positioning of the same with respect to the user's eyes.
Generally HMD optics trains adapted to project images on a helmet are mounted on the left and right sides of the exterior surface of the helmet at a level that is substantially aligned with the level of the wearer's eyes. See for example, U.S. Pat. No. 5,299,063. In this example, the mounting of the HMD on the sides of the helmet, and furthest away from the centerline of the helmet will result in a greater increase of the moment of inertia (MOI) for the combination of HMD and helmet, and as such, can pose an increased risk of neck strain or injury to the wearer.
It is apparent from the foregoing that the overall mass of the HMD optics trains and the positioning of the same on the helmet are integral to the performance of the same and the wearer. Thus, there is a need for an HMD system that provides a more compact HMD optics train that has a decreased overall mass compared to that of existing systems, and can be positioned on the helmet so as to minimize the increase in the moment of inertia associated with the added mass to the exterior surface of the helmet.